Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics
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Supporting information
Structure and bonding of the gold-subhalide cluster I-Au144Cl60[z]
Alfredo Tlahuice-Flores,* David Black, Stephan B. H. Bach, Miguel José-Yacamán, Robert L. Whetten*
Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio,
TX, 78249.
email: [email protected], [email protected]
Part I. Experimental Methods.
Part II. Theoretical Method.
Part III. Tables S1 and S2. Analysis of the point group of the Au144 clusters.
Part IV. Figure S1 and S2. Bond lengths of Au144(SH)60 z and Au144Cl60 z clusters.
Part V. Table S3. Frontier orbitals of Au25Cl18[1-] and Au4Cl4[0] clusters.
Part VI. Figure S4. Calculated XRD diffraction patterns of the Au144 clusters.
Part VII. Table S4. Point group analysis of the various shells of the relaxed Au144Cl60 2+ with initial Ih core
(Pd145)
Part VIII. Figure S5. Illustration of the measurement of the special angles
Part IX.Figure S6. Energy level diagrams, as in Fig. 2, showing the occupancy of the orbitals of the Au144Cl60
[z]
, as optimized in charge states [8-] (above) and [2+] (below)
Part X. Figure S7. Au144Cl60 [z] cluster given as 6 strands (180 atoms) and Au24 cluster.
Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics
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PART I
EXPERIMENTAL METHODS AND MATERIALS
A. METHODS
The ESI-MS method employed follows essentially the procedure described by Tracy et al.1 except that infusion
without electrolyte (cesium acetate) was used to observe the high charge-state [4+] of the Cs-free clusters. [The
cluster samples were synthesized and characterized separately as described in the main text’s Reference 13.]
Briefly, we electrosprayed the analyte (clusters) out of 50:50 methanol-toluene. In the methanol was typically
dissolved 100-mM cesium acetate (hereafter ‘electrolyte’). In the toluene was dissolved ~ 1-mM of the cluster
sample (hereafter simply ‘analyte’). So when the two solutions are combined 1:1, the working solution is 50
mM electrolyte and 0.5 mM analyte. Although these concentrations are those described in Ref. 1 for Au25
clusters, they worked well to identify the signal at expected parent ion mass-to-charge ratios for the massive
species described here, after which the concentrations were adjusted (as described below).
The instrument is a commercial electrospray ionization time-of-flight mass spectrometer (ESI-ToF-MS),
namely Bruker ‘MicroToF’, prior to the ToF analyzer. [It has a hexapole ion guide for ion focusing prior to the
‘pusher’ of the ToF.] For all these measurements, the instrument was optimized iteratively to high-mass
operation using cesium-triiode (in methanol) which forms clusters ranging to m/z > 10,000. To obtain the higher
m/z ions it is important to increase the hexapole’s radiofrequency (RF) voltage to its maximum value (800-V
peak-to-peak).
Under the described conditions, the distribution of detected ions (various charge-states and degrees of Cs-ion
attachment) appears rather similar to that published previously by Qian and Jin,3 wherein Au144(peth)60 species
were identified in the [2+] and [3+] charge-states and the Cs-ion numbers peaked at 3 or 4 attached ions. Under
these conditions, the low-mass range is dominated by a long series of peaks attributable to electrolyte clusters.
To obtain the results shown in Fig. 2, one infuses without cesium acetate but with all other ESI-MS
instrumental and solution conditions identical. In practice, this means that the operating conditions are first
established as above, then rinsed with electrolyte-free solution, and finally replaced this by analyte solution to
which no electrolyte had been added. Generally, repeated analyses on various days by the same operator (DB)
demonstrate that some persistence and care is required to establish the conditions whereby the mass spectra
have the signal-to-noise evident in Fig. 2.
The main panel of Figure 2 shows the mass spectrum obtained with electrolyte-free infusion over a wide range
of m/z, < 7 to > 13 kDa/z, which encompasses the expected m/z for the Au144(peth)60 species in the z = 3+ to 5+
charge-states. At the low end, the elimination of the electrolyte-cluster signal (see above) allows the features
indicated to be prominently identified. Beyond the high end, the [2+] features are also strongly reduced.
The principal species are identified as indicated by the labels in this main panel: the (144,60)[3+,4+] ions, along
with the ions attributable to a reaction byproduct (130,50) in the same two charge-states.2 The inset panel
contains expanded views of the regions selected to show the assignment of the charge-states and the shapes of
the peaks, consistent with natural isotopic abundances. Minor features are attributed to expected fragments and
slight contamination by residual electrolyte.3,4 Note that [5+] ions are not detected at all.
Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics
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PART II
THEORETICAL METHODS
We use a theoretical approach based on Density Functional Theory (DFT) to perform the structural relaxation of
the Au144(SR)60z clusters based on Lopez-Acevedo et al. model5 and the Pd145 structure by Dahl.6 The proposed
initial structures held a perfect I symmetry (with an Ih core for structure derivates from Dahl cluster) and were
considered relaxed when a 0.01 eV/Å value in force was obtained. The methodology of the optimization stage
used a double-ζ polarized basis set, the Perdew-Burke-Ernzehorf (PBE)7 parametrization for the exchangecorrelation functional, within the generalized gradient approximation (GGA), and a Troullier Martins scalar
relativistic norm-conserving pseudopotentials8 as implemented in the SIESTA package9. In the case of the -SH
ligand, during the optimization stage, hydrogens bound to the sulphur atoms orientate on trans positions but I
symmetry was maintained as can be verified by applying a 0.1 Å tolerance in position of the Cartesian
coordinates.
REFERENCES
(1) Tracy, J. B.; Crowe, M. C.; Parker, J. F.; Hampe, O.; Fields-Zinna, C. A.; Dass, A.; Murray, R. W. J. Am.
Chem. Soc. 2007, 129, 16209–17215.
(2) Chaki, N. K.; Negishi, Y.; Tsunoyama, H.; Shichibu, Y.; Tsukuda, T. J. Am. Chem. Soc. 2008, 130,
8608–8610.
(3) Qian, H.; Jin, R. Nano Lett. 2009, 9, 4083-4087.
(4) C. A. Fields-Zinna, R. Sardar, C. A. Beasley and R. W. Murray. J. Am. Chem. Soc., 2009,131, 16266.
(5)
opez- cevedo, . kola, . hetten, R. . r nbeck, .
kkinen, H. J. Phys. Chem. C 2009, 113,
5035.
(6) Tran, N. T.; Powell, D. R.; Dahl, L. F. Angew. Chem., Int. Ed. 2000, 39, 4121– 4125.
(7) Perdew, P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865-3868.
(8) Troullier, N.; Martins, J. L. Phys. Rev. B 1991, 43, 1993-2006.
(9) Soler, J. M.; Artacho, E.; Gale, J. D.; García, A.; Junquera, J.; Ordejón, P.; Sánchez-Portal, D. J. Phys.:
Condens. Matter 2002, 14, 2745-2779.
Ref 13 in manuscript: Bahena, D.; Bhattarai, N.; Santiago, U.; Tlahuice, A.; Ponce, A.; Bach, S.B. H.; Yoon B.;
Whetten, R. L.; Landman, U.; Jose-Yacamán, M. J. Phys. Chem. Lett., 2013, 4, 975–981.
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PART III
Tables S1 and S2. Analysis of the point group of the Au144 clusters.
Au144Cl60[z]
Tolerance (Å)
Point group
Neutral, z = 0
0.12
C2
0.13
I
Dication, z = 2
0.04
C2
0.14 eV more stable than Ih core
one (from Dahl structure)
0.043
I
Tetra-cation z = 4
0.041
D5
0.043
I
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Au144(SH)60[z]
Tolerance (Å)
Point group
Neutral (z=0)
0.05
C2
0.07
D2
0.094
I
0.048
C2
0.068
D2
0.11
I
0.001
C1
0.01
C1
0.035
D5
0.036
I
Spin polarized (z = 0)
Dication (z = 2)
In both tables are given the small tolerance in position in order to obtain an I symmetry.
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PART IV
Figure S1. Bond lengths of the Au144(SH)60z clusters.
Figure S2. Bond lengths of the Au144(Cl)60z clusters.
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PART V
Table S3. Frontier orbitals of Au25 and Au4 clusters.
Cluster
HOMO-LUMO gap,
eV
HOMO levels, eV
LUMO levels, eV
Au25Cl18- (Th point group)
1.18
-3.51, -3.51, -3.51
-2.33, -2.33
Au25(SCH3)18- (Ci)
1.32
-2.32 -2.32 -2.28
-0.96 -0.92
Au4Cl4 (D2d)
3.42
-5.83 -5.83
-2.41
Au4 (SCH3)4 (D2d)
4.6
-5.32
-0.72
Results shown in Table S3 are in agreement with Table 3 of references: D.-E. Jiang, M. Walter, Nanoscale
2012, 4, 4234-4239.
Table S4. Frontier orbitals of Au144 clusters.
Cluster
HOMO-LUMO gap, eV
HOMO levels, eV
LUMO levels, eV
Au144(SH)60 neutral
0.10
-3.73 -3.70
-3.69 -3.68 -3.67
Spin polarized
0.03
-3.73
-3.70 -3.69 -3.68 -3.67
Au144(SH)60 dication
0.12
-5.17
-5.05 -5.05 -5.05 -5.04 -5.04
Au144Cl60 neutral
0.04
-4.56
-4.52 -4.51 -4.51 -4.49
Au144Cl60 dication
0.2
-5.17
-4.97 -4.97 -4.96 -4.96 -4.96
It is evident from Table S4 that Au144Cl60 with [2+] charge holds more degenerate electronic levels indicating a
more symmetric structure. In the [4+] state, the HOMO is 5-fold degenerate (-6.00 eV) and the LUMO is nondegenerate (-5.64 eV), such that the gap is +0.36 eV.
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PART VI
Figure S4. Calculated structure-factors (relating to XRD diffraction patterns) of the Au144 clusters.
The colours denote: (black) Au144(SH)60[0]; (red) Au144(SH)60 [2+]; (blue) Au144Cl60[0]; (green) Au144Cl60 [2+].
The good overlap emphasizes that, at low resolution, the ordering is common to all structures examined.
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PART VII
Table S4. Point group analysis of the various shells of the relaxed Au144Cl60[2+] with initial Ih core (Pd145)
Cluster
Tolerance (Å)
Point group
Au144Cl60 [2+]
0.032
C3
With initial Ih core
0.033
T
0.034
I (it never holds Ih)
0.025
C2
0.028
D5
0.035
I
0.42
Ih
0.016
C2
0.019
D5
0.021
I
0.023
Ih
0.027
C2
0.028
D5
0.034
I
0.42
Ih
0.0037
Ci
0.0069
C2h
0.0079
D2h
0.0088
Ih
0.015
C2
0.02
D5
0.021
I
0.023
Ih
0.03
C2
0.031
T
0.033
I
Au114
Au54
Au60
Au12
Au42
Cl60
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PART VIII
Figure S5. Determination of the special angles in the Au144Cl60 [4+] cluster.
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PART IX
Figure S6. Energy level diagrams, as in Fig. 2, showing the occupancy of the orbitals of the Au144Cl60 [z], as
optimized in charge states [8-] (above) and [2+] (below).
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PART X
Figure S7. Au144Cl60 [z] cluster given as 6 strands (180 atoms) and Au24 cluster.